US 20040233783 A1 Abstract A method for processing echoes in a time-of-flight ranging system or level measurement system. The method comprises an initial noise floor level and identifying potential echoes in an echo signal above the initial noise floor level and a noise signal below the initial noise floor level. One or more portions of the initial noise floor level are modified and an adjusted noise floor level is generated by applying a cubic spline algorithm to the modified portions and the initial noise floor level. The adjusted noise floor level is then used to identify valid echoes in the echo signal and generate an echo signal profile.
Claims(7) 1. A method for generating an echo profile in a time-of-flight ranging system, said method comprising the steps of;
(a) transmitting a transmit burst of energy to a reflective surface; (b) receiving reflected pulses from said reflective surface, and converting said reflected pulses into an echo signal; (c) establishing an initial noise floor level; (d) identifying one or more portions of said echo signal above said initial noise floor level as having potential echoes; (e) modifying one or more segments in said initial noise floor level, and generating an adjusted noise floor level; (f) wherein said step of generating comprises applying a cubic spline procedure to said modified segments and said initial noise floor level; (g) identifying valid echoes in the portions of said echo signal above said adjusted noise floor level; and (h) generating an echo profile using said identified valid echoes. 2. The method as claimed in 3. The method as claimed in 4. A method for generating a noise floor level for an echo profile in a time of flight ranging system, said method comprising the steps of:
(a) establishing an initial noise floor level; (b) modifying one or more points in said initial noise floor level; (c) applying a cubic spline algorithm to said modified points and said initial noise floor level to generate a plurality noise floor data points; (d) sampling said noise floor data points; (e) forming an adjusted noise floor level from said sampled noise floor data points. 5. The method as claimed in 6. The method as claimed in 7. A method for generating an echo profile in a time-of-flight ranging system, said method comprising the steps of:
(a) transmitting a transmit burst of energy to a reflective surface; (b) receiving reflected pulses from said reflective surface, and converting said reflected pulses into an echo signal; (c) establishing an initial noise floor level; (d) subtracting said initial noise floor level from said echo signal to identify one or more potential echoes; (e) modifying one or more segments in said initial noise floor level, and generating an adjusted noise floor level; (f) wherein said step of generating comprises applying a cubic spline procedure to said modified segments and said initial noise floor level; (g) subtracting said adjusted noise floor level from said echo signal to identify one or more valid echoes said echo signal; and (h) generating an echo profile using said identified valid echoes. Description [0001] The present invention relates to signal processing, and more particularly to a method for echo processing in level measurement or time of flight ranging systems. [0002] Pulse-echo acoustic ranging systems, also known as time-of-flight ranging systems, are commonly used in level measurement applications. Pulse-echo acoustic ranging systems determine the distance to a reflector (i.e. reflective surface) by measuring how long after transmission of a burst of energy pulses the echoes or reflected pulses are received. Such systems typically use ultrasonic pulses or pulsed radar or microwave signals. [0003] Pulse-echo acoustic ranging systems generally include a transducer and a signal processor. The transducer serves the dual role of transmitting the energy pulses and receiving the reflected energy pulses or echoes. The signal processor is for detecting and calculating the distance or range of the object based on the transmit times of the transmitted energy pulses and the reflected energy pulses or echoes. [0004] Since the reflected energy pulses or echoes are converted into distance measurements, any errors in the echoes result in distance measurement errors which degrade the accuracy of the level measurements. [0005] Accordingly, there remains a need to provide a system and techniques which improve the processing of the reflected energy pulses or echoes. [0006] The present invention provides a method for improved echo processing, and comprises a method for generating a new noise level signal which is based on the original noise level and any changed or modified portions. [0007] In a first aspect, the present invention provides a method for generating an echo profile in a time-of-flight ranging system, said method comprising the steps of: (a) transmitting a transmit burst of energy to a reflective surface; (b) receiving reflected pulses from said reflective surface, and converting said reflected pulses into an echo signal; (c) establishing an initial noise floor level; (d) identifying one or-more portions of said echo signal above said initial noise floor level as having potential echoes; (e) modifying one or more segments in said initial noise floor level, and generating an adjusted noise floor level; (f) wherein said step of generating comprises applying a cubic spline procedure to said modified segments and said initial noise floor level; (g) identifying valid echoes in the portions of said echo signal above said adjusted noise floor level; and (h) generating an echo profile using said identified valid echoes. [0008] In a further aspect, the present invention provides a method for generating a noise floor level for an echo profile in a time of flight ranging system, said method comprising the steps of: (a) establishing an initial noise floor level; (b) modifying one or more points in said initial noise floor level; (c) applying a cubic spline algorithm to said modified points and said initial noise floor level to generate a plurality noise floor data points; (d) sampling said noise floor data points; (e) forming an adjusted noise floor level from said sampled noise floor data points. [0009] In yet another aspect, the present invention provides a method for generating an echo profile in a time-of-flight ranging system, said method comprising the steps of: (a) transmitting a transmit burst of energy to a reflective surface; (b) receiving reflected pulses from said reflective surface, and converting said reflected pulses into an echo signal; (c) establishing an initial noise floor level; (d) subtracting said initial noise floor level from said echo signal to identify one or more potential echoes; (e) modifying one or more segments in said initial noise floor level, and generating an adjusted noise floor level; (f) wherein said step of generating comprises applying a cubic spline procedure to said modified segments and said initial noise floor level; (g) subtracting said adjusted noise floor level from said echo signal to identify one or more valid echoes said echo signal; and (h) generating an echo profile using said identified valid echoes. [0010] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying drawings. [0011] Reference is next made to the accompanying drawings which show, by way of example, embodiments of the present invention and in which: [0012]FIG. 1 is a graphic representation of an echo signal waveform, a noise floor level waveform and a noise signal waveform for a time-of-flight ranging system; [0013]FIG. 2 is an echo profile plot showing a noise level waveform adjusted in accordance with the present invention; [0014]FIG. 3 is an echo profile plot showing a valid echoes waveform determined according to the present invention; [0015]FIG. 4 is a flow chart showing a method for generating a noise floor level signal or waveform in accordance with the present invention; [0016]FIG. 5( [0017]FIG. 5( [0018]FIG. 6 is a flow diagram showing the data flow for performing echo processing according to the present invention; [0019]FIG. 7 shows in tabular form an input data array; [0020]FIG. 8 shows in tabular form an output coefficient data array; [0021]FIG. 9 shows in tabular form an output data array determined in accordance with the present invention; [0022]FIG. 10( [0023]FIG. 10( [0024] Reference is first made to FIG. 1 which shows in graphic form an echo profile plot indicated generally by reference [0025] The echo signal [0026] As will now be described in more detail, the subject invention is directed to a method or process for producing an improved receive echo signal [0027] Referring back to FIG. 1, the echo profile plot [0028] The noise floor level [0029] Reference is made to FIG. 2, which shows an echo profile plot indicated by reference [0030] The echo profile plot [0031] Reference is next made to FIG. 3, which shows the echo profile plot [0032] Reference is next made to FIG. 4, which shows in flowchart form a method for generating an adjusted noise floor level, for example of the adjusted noise floor level [0033] As shown in FIG. 4, the first step indicated by block [0034] The operation of the method or procedure for generating the adjusted noise floor level is further illustrated with reference to FIGS. [0035] There are two main types of data: input data and output data. The input data comprises an array of distances, and their corresponding amplitudes. The output data comprises an array of polynomial coefficients, which matches the input distances and amplitudes. The polynomial coefficients are applied to the cubic spline algorithm to obtain the amplitude associated with a distance. The flow between the input data [0036] Reference is next made to FIGS. 7, 8 and [0037] As described above, after the output data is created, a sampling operation is performed to obtain a specific finite number of points for the adjusted noise floor level. The sampling may be performed at any resolution. [0038] To find the amplitude for a specific distance, the following cubic equation is used: [0039] To choose the appropriate coefficients, the distance x is matched with the appropriate coefficients from the table in FIG. 8. For example, if the distance is 0.9, it is within the bounds of the first equation, i.e. 0.8<distance<2.12, and the coefficients are a=0.3, b=−0.5, c=0.2 and d=0.001. The amplitude value is given as: y=0.3x [0040] The final output data is stored in an array which is like the input data array, except there are more points covering the same distance. Exemplary output data with three points for every one distance point is shown in the table of FIG. 9. It will be appreciated that the more points sampled, the greater the precision of the adjusted noise floor level. [0041] A cubic spline algorithm is utilized to generate points for the adjusted noise floor level as described above. The cubic spline algorithm is used to create a series of cubic equations to represent the line of best fit for raw data points. The end result is ‘n’ finite points which are represented by ‘n−1’ cubic functions. The n−1 cubic functions are used to select an infinite number of points, and the function y=ax [0042] Pseudo Code Listing for Cubic Spline Algorithm [0043] © Siemens Milltronics Process Instruments Inc. 2002-2003
[0044] It will be appreciated that cubic splines are smooth functions and when used for interpolation these functions do not have the oscillatory behaviour of high-degree polynomial interpolation. Advantageously, cubic spline functions form a line that intersects every point which is desirable for the subject application. FIG. 10( [0045] The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Certain adaptations and modifications of the invention will be obvious to those skilled in the art. Therefore, the above discussed embodiments are considered to be illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Classifications
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